1. Field of the Invention
The present invention relates to a pulse width modulation (PWM) driving circuit and a PWM driving method, and more particularly, to a PWM driving circuit and a PWM driving method, which are feedback-controlled without a feedback loop, which is a secondary side, using a photo coupler.
2. Description of the Related Art
One of important specifications required for lighting devices using a light emitting diode (LED) as a light source is compatibility with a triac dimmer. In order to interconvert with the triac dimmer in an LED driving circuit having a switching mode power supply (SMPS) structure, a level of dimming must be detected to be reflected to a switch control signal.
Such a structure causes a decrease in line regulation performance. The line regulation performance is not required when the dimming is not performed.
When support for the triac dimmer is needed, a flyback structure shown in FIG. 4 may be used.
Here, a level of dimming is sensed by a photo coupler 600 to be reflected to a reference signal VREF, and thus, output control according to the level of dimming can be performed.
In a simple example, in this case, the reference signal VREF is varied in linear proportion to an input voltage VIN. Here, since the input voltage is reflected to the output, the line regulation performance is decreased.